Specific, efficient delivery of therapeutic and diagnostic compounds to cells, especially to the cytosol, is a major goal of many pharmaceutical companies. A number of different approaches have been utilized to increase specificity and uptake. For example, nanotechnology has been widely used in the development of new strategies for drug delivery and cancer therapy. PH-sensitive nano-systems have been developed in which drug release is specifically triggered by the acidic tumor environment and such systems can improve the efficiency of cancer treatment. Feng Wnang et al. develop a drug delivery system by tethering doxorubicin onto the surface of AuNPs with a poly(ethylene glycol) space via an acid-labile linkage (American Chemical Society, 2011, Vol. 5, No. 5, pp. 3679-3692). Tian-Meng Sun et al., discloses a cancer stem cell therapy using doxorubicin conjugated to gold nanoparticles via hydrazone bonds (Biomaterials 35, 2014, pp. 836-845). US 2013/0331764 relates to a method for delivering an anticancer drug into cancer cells by binding the anticancer drug to pH-sensitive metal nanoparticles so as to be separated from cancer cells. WO 2013/139942 provides a nanoparticle comprising a metal nanoparticle and at least one linker.
However, there is still a need to develop a pH-sensitive delivery system having better efficacy.